1. Technical Field
The present disclosure relates generally to micromachined devices and methods of assembly the same. More particularly, the present disclosure relates to structures and methods for precisely aligning substrates (and the micro-components disposed thereon) which lack complimentary interfacing/inter-engaging surfaces or features.
2. Background of Related Art
Many manufacturing techniques rely on precise alignment techniques to ensure accurate inter-working relationships and/or proper inter-working connections among the various components of the finished product. As can be appreciated, even the slightest aberration or misalignment between two inter-working components can render the end product virtually unusable for its intended purpose.
Modern trends towards miniaturization and other advancements in telecommunications, microelectronics, micro-mechanics and fiber optics have made alignment tasks more daunting by requiring highly precise alignment of the various micro-components disposed thereon, e.g., microelectronic and micro-optic components such as transistors, wires, lenses, fiber optic cable arrays, etc. For example, integrated circuit chips must be aligned with respect to circuit boards so that they may be soldered or otherwise connected to an electrically conducting pattern on the circuit board. Moreover, optical fibers and micro-lenses must be precisely aligned with respect to each other (or with respect to a light source) so that light may be effectively transferred through the optical fibers or lenses.
As can be appreciated, a number of techniques have been developed to position two or more components relative to one another on a substrate (silicon chip). One such techniques simply involves placing one component atop the other component and subsequently aligning the two components on the chip. Once the components are properly aligned, they are permanently attached to the substrate by a known method of attachment, e.g., adhesives or solder bumps. Generally, this technique is limited to uses where relatively imprecise alignment is acceptable.
Other advances in technology have greatly improved alignment accuracy among micro-electronic and/or micro-optic components, e.g., photolithographic or etching techniques. These techniques are particularly suited for self-alignment or so-called “passive” alignment of various micro-machined components and devices. See, for example, U.S. Pat. Nos. 4,558,812 and 5,178,723 for descriptions of known self-alignment techniques.
For example, a number of assemblies which utilize a single crystal semiconductor material, e.g., silicon, as the support structure for the various optical devices are known in the optics industry. This is often called “silicon optical bench” technology. Silicon processing technology has been developed to the stage where a number of relatively simple procedures, e.g., oxidation, isotropic or anisotropic etching, may be utilized to facilitate attachment of the various optical lenses and optical fibers to the support member as well as provide precise alignment therebetween. Additionally, it is possible to form optical waveguiding structures directly in or on a silicon substrate thereby resulting in the ability to form a completely operable optical subassembly in silicon.
Passive or self-alignment of microelectronic, micro-mechanic or micro-optic components on substrates which have complimentary or interengaging surfaces on opposing surfaces (i.e., frontside to frontside surfaces) has proven to be relatively simplistic. For example, a series of alignment spheres (e.g., ball lenses) can be interposed between two micro-etched channels disposed on (or within) respective substrates. More particularly and as best illustrated by way of example in FIG. 1, aligning two silicon chips 20 and 30 which include opposing patterned surfaces, i.e., facing surfaces or so-called “frontside to frontside” opposing features, is relatively simplistic. For example, one or more alignment spheres 40, e.g., ball lenses, may be interdisposed between complimentary pits, grooves, cavities or patterns 22 and 32 which are micromachined, e.g., anistropically etched, within each corresponding substrate's 20, 30 surface. Each lens self-aligns (self-centers) within a respective channel according to pre-determined tolerances which, in turn, accurately aligns the two substrates 20 and 30 (and the respective micro-components disposed thereon) relative to one another (See FIG. 1 wherein the ball lenses 40 accurately align the stacked chips 20 and 30 relative to each other for subsequent bonding).
FIG. 2 illustrates the inherent frustrations associated with precisely aligning microelectronic, micro-mechanic and micro-optic components on substrates which do not have opposing surfaces, i.e., so called “frontside to backside” alignment. As can be appreciated, aligning the micro-lenses 50 on substrate 20 with the grooves 32 of substrate 30 requires backside alignment on the lens substrate 20. Typically, alignment tolerances for corresponding micro-mechanical, microelectrical and micro-optical components are on the order of about 1 micron (or better) for achieving optimum communication between components.
Thus, a need exists to develop relatively inexpensive and reliable structures and methods which precisely align microelectronic, micro-mechanical and micro-optical components disposed on one or substrates which do not include mechanically-patterned or mechanically inter-engagable opposing surfaces.